Method and apparatus for detecting fissures in rail



R. W. MOKEE Oct. 9, 1956 5 Sheets-Sheet 1 Filed Nov. 15. 1951 y e Q M I Q om NW mm a QM m Wm wh .B. 0 Kim/ w w w w wvi 43 Oct. 9, 1956 R. w. MOKEE 2,766,424

METHOD AND APPARATUS FOR DETECTING FISSURES IN RAIL 5 Sheets-Sheet 2 Filed NOV. 15, 195} 70 r .3. 66 l a a T p TEE-LIN 'II II INVENTOR 7g @Rllfhani 1M [fa fee United States Patent lVIETHOD AND APPARATUS FOR DETECTING FISSURES IN RAIL Richard W. McKee, Chicago, Ill., assignor, by mesne assignments, to Teleweld, Inc., a corporation of Idaho Application November 15, 1951, Serial No. 256,501

'12 Claims. 01. 324-37 This invention relates to demagnetization of the top surface of a rail ball in a sustained magnetic field, more particularly in a sustained trailing magnetic field of the type disclosed in copending United States patent application Serial No. 628,146, filed November 13, 1945, now Patent No. 2,622,131. It involves both apparatus and method. It employs an alternating current magnet, but of comparatively high frequency. The invention also relates to the position of the pickup coil in the magnetic flux circuit, that is, the distance from the main magnet creating the trailing sustained field.

For those not acquainted with rail fissure detection, the most significant way of classifying the various methods of fissure detection for the purposes of this application is to separate those that are testing changes in a moving flux field from those that are testing changes in a fixed flux field. The Sperry and Teledetector systems are of the first type. In the Sperry system, the current in the rail between the two sets of brushes sets up a moving flux field around the rail in which rides the pickup moving with the field. The pickup moves with the flux, and so long as the field continues symmetrical, the pickup cuts no lines of force and generates no signals. Where a portion of a rail containing a fissure enters the flux circuit, the current in going around the fissure changes the flux field pattern above the rail, and since the relationship of the pickup to the rail ball remains constant, the changing flux field generates a potential in the pickup. The field moves through the pickup.

The Teledetectcr system is similar. In this system a flux field is projected rearwardly (and forwardly) of the magnets. The flux field includes the rail ball and as viewed from the side as the car moves along the rail, so long as the rail is perfect, the field pattern is perfect. The pickup is at a certain position in this field, and it cuts no flux because the flux of the field is moving with it. As Chester McKee has defined the trailing sustained field system, The flux lines are a sustained standing pattern with the coil mounted within that sustained pattern and it requires a flaw of some description to change the flux pattern in order to create a signal.

In the second class are those that are testing changes in fixed flux fields. The outstanding system of this class is that of the Association of American Railroads (A. A. R.), wherein a rail is magnetized, leaving a residual field, and thereafter a pickup is moved through the residual field. In the case of a perfect rail, "after the pickup has reached a constant speed, it will generate no E. M. F. Not until the density or angularity of the flux in the field varies, will the pickup generate a signal.

The preceding three paragraphs are pertinent to this application because the principal object of this invention is to eliminate signals derived from harmless surface defects in order to lighten the rail observing load for the operators, and thereby to eliminate false stops by the car during the exploratory step. This object is attained in the second method of testing by demagnetizing the surface skin of the rail ball by using an alternating current mag- 2,766,424 Patented Oct. 9, 1956 net. But presumably an A; C. magnet is effective for residual testing only for only in this method has it been used. Billstein, in United States Patent No. 2,218,784, shows a 60-cycle A. C. magnet positioned between the trailing magnet and the flux responsive means in a residual magnetic field system, that is, the A. A. R. system. Similarly, the A. C magnet 46 shown in Fig 1, Sheet 1, of United States Letters Patent No. 2,388,683, to Royal Frickey and Chester W. McKee, is positioned ahead of all testing equipment and is demagnetizing residual magnetism.

One does not think of adapting the A. C. magnet to a sustained flux field system of either the Sperry or Teledetector types because the mind immediately encounters a bar or block, the A. C. magnet is working against forces greater than its own. In the Sperry system, the field above the rail varies with the differences in the paths of the current through the rail ball, and while it is doubtful that an A. C. magnet would appreciably affect the path of the current in the ball immediately beneath the growler, it is reasonably certain thatthe current would flow through that portion of the rail adjacent to the pickup without being influenced by the A. C. magnet. The same would be true of Teledetectors trailing sustained field system excepting for a time lag for repolarization and the fact that the trailing sustained field is declining in strength as the magnet moves away. Whereas in the Sperry system, the field between the brushes is of constant strength with constant E. M. F. being applied to it so that an A. C. magnet would onlyafliect'the rail immediately adjacent its poles, in the Teledetector system the field is declining United States Letters Patent No. 2,388,683 or in co-' pending application Serial No. 749,166, for here magnet assemblies Nos. 1 and 2 weigh 2,000 pounds each, and the main magnet assembly weighs 3,500 pounds. These are the weights of the magnets for each rail. No longer is the trailing sustained field imperceptible three feet behind the main magnet, but it is pushed out thirty feet and this despite interpositioning of standard 33"'magnetic car wheels. Polarization of the top rail ball skin is very strong and the bums, shelley spots, flows, and the like generate strong potential signals in the amplifier. However, after the A. C. magnet demagnetizes a burned spot or other surface defect, the only way of remagnetizing the burned spot is by the trailing sustained field. This requires time and additionally, the trailing sustained field is steadily declining in strength.

Another object of this invention is to position the pickup coil in the trailing sustained field at the optimum point where variations in that field will produce a signal of maximum strength in the pickup. Heretofore, applicant positioned the pickup in the trailing sustained field by a cut and try method but now the pickup is positioned in that field at the point where the flux is leaving the rail at substantially right angles to the surface of the ball.

In the drawings,

Fig. 1 is a scale schematic illustration showing the correct relative, longitudinal dimensions of the three direlative spacings of these five units for practicing the present invention;

Fig. 2 is a side elevation of the detector carriage and the A. C. magnet showing more exactly its relation to the pickup coil;

Fig. 3 is an end view of the carriage;

Fig. 4 is a theoreticalillustration of the depth-cf will forma circuitrearwardly through the .rail '54 and. I

Fig. 6 is like Fig. excepting thatit assumes thartherehas been an alternating current demagnetization immediatelyin advance of the pickup.

Continuing to refer to the drawings, and particularly to Figure. 1, the car 10 is supported ontwo trucks 1 -2. and,14. The front of the-caris designated-by the numeral l6. ,-Disposed between the.cartrucks 12 andn14 aIe three magnet-bearing trucksr18, and 22.; Each of these latter is;a true truck and consists of a generally rectangular frame-supportedby pairs of wheels, each pair being non-rotatably mounted on a shaft,-. the nearwheels ,of each truck being-designated and; 28 and:

engaging the rail 3Q as shownin Fig-1;.

For this invention, therelative size tof the magnets,"

their polarity, and their spacingare important. All. of the rnagnetsv are direct current magnets, are constructed of similar elements and are,connected to a common of the w-iren-in the windings together ;with the-electroe motive force across the windings of eachicore are approximately thesame in all of the magnets; Themagnet-3 2, c alled-the first magnet, consists of three vertical iron cores with theirqthreetop poles tied together by an iron bar and their .three bottom poles tied together by an iron bar, as is suggested by the cut-away portion of the'mainmagnet-M, wherein a vertical ,iron

core 36 tied to a lower iron bar 38 andartop iron.

bar 40. r

The. lower pole. of the first magnet 32 is north. For a reasont that is. not clearly understood, where three directzcurrentmagnets of the types-32, 42 and 44 are used, the main magnet 44 should. have its lower pole a north whichaon the basis of rocking the molecules in the rails means that the lower .pole of the first magnet musthalso be aanorth ,(see copending application Serial tained field. is set up by a-south pole on the main magnet,,-..but for a reasomnot clear to applicant, they -do not obtain from. this trailing-sustained field resultsas The'car has been'tested by reversing w the polarity of all three magnetsso that the trailing susgood'as thosefroma field created by magnets of north, 1 south and north. polarities respectively.- The second magnet 42 is identical with the first magnet 32, excepting that'the windings and hence the polarity is reversed- The magnetsshown in Fig.1 are'in no way related to the magnets on the far rail. There are two independent magnets mounted on each truck. -The magnets on onerail are wired through switchesso that all three be simultaneously energized.-

The :main magnet 44 has six vertical cores and its cores and windings are similar to the cores and windings of the first-andsecond magnets. -In theory, the mairrmagnetis twiceias'powerful as the first-'orthe second magnets. ThefirsQand-second magnets are spaced --by a distanceof seven feet-which -will be considered as X; while the second :and main magnets-arespaced by the distance 2X,

or approximately fourteen feet.

ing for the momenbthe effect-upon the molecules in the rallza portion of the flux circuit of the leadingportion of the first magnet 32 willestablish a' leading sustained- The theory of this-'arrangement of the direct current magnets is this.- Ignorfield through therail at 46 and the air at 48 andthence backrto the upper pole ofthe same magnet." 'More' than-- half of the flux from the first magnet, howevenwill move down the rail at 49 to the lower pole of the second magnet 42, which is a south'pole. A third flux circuit will be established between the trailing pole portion of the second magnet 42 through the rail portion 50 to the leading north pole portion of the main magnet 44. Substantial quantities of flux will move along the paths 50 and 52. Most of the flux from the main magnet this fiux will be pushed well back intothe rail. 'This main magnet forms the moving flux circuit which includes the magnet, therail and the air above t-he rail, and

not attachedto truck 14, but function independently of eachother and the car truck. They are raised. and low-H ered by air cylinders 64 and pistons 66 on telescoping t.

guides .68 and 70.

In its lowermost position, a detector carriage 62 rides fireely .on .two .flangedwheels 72 and 74 whose flanges.

are pressed against the gauge side. of the rail by the 'telescopingguides 68 and.70. Rigidly fastened by any suitable .meansto the detector carriage 62 immediately.

behind .the wheel 74 is an alternating current magnet.

C generatotw'rhe size eachwertical .coreinthe: Q 76 consisting of two vertically positioned flux conductive numberoli windingson-each vertical. core, and the 1812f cores 7.8 and 80., see Fig. 2, whosemagnen'cally reinforcing conductive windings are connected to each other in series,' and.by conductors 82 and 84 to an alternating currentgcnerator 86. The'frequcncy of this generator is 900 cycles per second. its poles are spaced from the rail by about one-fourth inch and it operates on a voltage of 200 to 250 depending; upon the size of the rail. The distancefrom the trailing pole of the main magnet 44 to the alternating current magnet 76 is approximately ten feet or 1 /2 X.

Independently suspended from the detector carriage 62 is the pickupicarriage 35 which carries the pickup coil 99 and which rides along the rail on sets of wheels 92 and 94. The distance. from the pickup coil to the trailing edge of the alternating current magnet 76 is approximately eighteen inches or A X.

This application is not concerned with the details of constructionpf any of the magnets or their trucks or of the detector carriage or pickup carriage or its methodof' suspension. Consequently, these construction details .are shown somewhat schematically in the drawings and are not described. The correct relative longitudinal dimensions. of the magnets, pickup coil and alternating; current magnet are shown in Fig. l and the spacing shown 'isniinpo-rtant within a limitcd rangc, Thef",pickuproarriage is longitudinally fixed (substantially, "there being a little lengthwise play) with respect to the car, and.the trailing main truck 14. The axles. on this truck are on eight toot centers- The car itself 72 teetlong. The main'magnet truck is on wheel shafts on nine and a halfto'ot centers and the first and second, magnets are on trucks on which the shafts are spaced by six and one-quarter feet. The Wheels 57 and 59 of the truck 14 are standard 33 car wheels and are magnetic.

Applicants problem. was to provide the desired spacing of X and; 2X betwee ti c three magnets and then to positi n the pickup coil reasonably close to the trail: ing magnet. The elect-romotive force generated by these magnets is so great that the field extends well behind the car,:t'nirty feet behind the main magnet. Dip needle tests were made on the trailing sustained field at the Union Pacific test track at Valley, Nebraska, and it was found that the fiux is leaving the rail at substantially right angles between the wheels of the trailing car "truck; -T'hese' car truck wheels are magnetic and the -leading wheel shunts a portion of the flux through itself-andthereby-shortensthe trailing sustained field.

This application is the first to disclose atfith'e pickup coil should be positioned in the flux circuit as close to the point where the angle of emersion of the flux leaving the rail ball is at right angles to the ball surface as best result was obtained from a frequency of 900 cycles and several test runs on the same track wherein the characteristics and positions of fissures and surface defects are exactly known resulted in a showing of a 62 percent possible. Heretofore, applicant as positioned the pickup 5 reduction in visual indication markings derived from surcoil in the trailing sustained field by a cut and try method, face defects. and this method has been useful in getting the pickup Testing also considered the effect of the spacing of coil near the best point, which is where the flux is leavthe pickup 90 behind the alternating current magnet 76. ing the rail ball at right angles to its surface. In copend- This spacing must be sufiicient when considered with ing application Serial No. 749,166, the fiux is shown leav- 10 the electromotive force in the alternating current magnet ing the rail at an obtuse angle (with respect to the magso that the alternating magnetic field itself will not affect net 18). -Applican-t does not now believe that this 'appl'ithe pickup. On the other hand, this being a trailing suscat-ion shows a true picture of the field, nor does he tained field, the pickup must be sufficiently close so that wholly agree with the statements made at that time the flux flowing deep in the rail will not have the time found on page 5 of that application. In 1947, the pickup to repolarize the surface defects. The trailing sustained coil was not being positioned in the moxing flux field field is a weakening one and this taken in conjunction by means of a dip needle. This instrument has been with the normal lag in time for flux to effect polarization used y recently- The action of 11116 p needle as if of molecules accounts in part for the success of the sys- IHWBS y from an upright pole piece having a north term. The accompanying chart illustrates generally the pole adjacent o the rail is this! y, the S01E11 20 results of tests made at Valley, Nebraska, with four dif- 19016 of "114% p needle P n anglfi M the 501mm ferent frequencies with the current running at eight miles of the P Wifih the p needleis north P extending an hour. The best results were obtained with the A. C. angularly outwardly :as indicated by the arrow 120 in magnet operating on a frequency of 900 cycles, the tape Fig. 1. As the dip needles moves away from the pole, showing 62% less indications from surface defects than it assumes a more and more erect position until it is were shown by the same apparatus run over the same vertical, as at 122. Thereafter the =S0lll3h P018 is farther piece of track with the A, C, magnet unenergized,

' Magnetic Duration of Duration of Duration of Sustained ?No. of Polarity Rebuild Percentage of Speed of car along the rail North South North Rea-Polarization Changes by A. 0. between A. 0. Surface Defects Polarization Polarization Magnet Magnet; and Suppressed 32 at 800 cycles Appreciable.

Smiles per hour, 142 per second- %second- 1 second '3 seconds (approximately). 2; 3% 3%3Xggi; ff

' 47 at 1,100 cycles Little or no Su-p pressron.

l The A. C. demagnetization occurs about one second after the beginning of the sustained North repolarization.

away from the magnet, as at 124, and ultimately the dip needle .assumes a horizontal position with its north pole pointed toward the magnet. Actually, before this occurs, the dip needle comes under the influence of and its position is controlled by the earths magnetic field. The flux leaving the ball vertically is in flux circuits that are deep in "the rail ball, i. e., 108 in Fig. 6, and hence from flux circuits that are affected by internal fissures.

The frequency of the alternating current magnet is 900 cycles per second. It is reasonably clear that an effective frequency is determined by several factors, i. e., the speed of the car along the mail, the strength of the trailing sustained field at the point behind the main magnet at which the alternating current magnet is lorated, the electrornotive force of the alternating current magnet itself, and undoubtedly the size of the cross sectional area of the rail ball. perimented in three ways after first spacing the pickup coil from "the main magnet so as to give optimum results on the recording tape in the cab. Firstly, the frequency of the alternating current magnet has been widely varied. Operating on standard cycles with the car moving at eight miles an hour, no appreciable effect on the strength of potential signals generated 'by surface defects such :as burns was perceived. Increasing the frequency to 800 cycles per second appreciably reduced misleading signals from surface defects. His tests further showed that a frequency in excess of 1100 cycles per second did not result in a sufiicient improvement to Warrant demagnetizing. Operating the car at eight miles an hour, he concluded that in a range of 750 cycles to 1050 cycles, an alternating current demagnetizer was worthwhile. In tests at Valley, Nebraska, the car with the magnets arranged as shown in Fig. 1, ran the track with the demagnetizer unenergized, and then immediately re rau the track with the demagnetizer energized, The

Applicant has ex- 1 Accelerating the speed of the car will reduce the duration of the three polarizations. At the same frequencies shown in the chart, the changes in polarizations of the rail ball will be correspondingly increased, which means that the optimum frequency will be lower than 900 cycles found desirable at eight miles an hour. Conversely, if the speed of the car is decreased, the optimum frequency for the alternating current should be higher.

Some theoretical explanation for the operation of the system may be helpful. In Fig. 4, there is schematically illustrated the two poles 78 and 80 of the alternating current magnet 76 adjacent a rail ball with flux in the air and flux 102 in the upper skin of the ball. The comparatively slight penetration of the flux from the alternating current magnet 76 circuit into the ball surface is due in part to the electromotive force in the magnet, in part to the spacing of the poles above the rail, in part to its speed of movement along the rail, but primarily to the number of changes in polarity which occur per second. In other words, the reason that applicant obtains unsatisfactory resultsfor frequencies above 1100 is that the time in which the flux flows in a single direction is too short to substantially penetrate the ball skin. When the frequency is dropped below 750 cycles, it is believed that here the alternating flux circuit is able to penetrate the rail ball more deeply and this further weakens the trailing sustained field.

Referring now to Fig. 5, the rail ball 102 has in it a burn 103. Where there has been no alternating current demagnetization, the lines of force leaving the rail become steadily fewer as illustrated by the spacing between lines 104 and 106 as compared with the spacing between 108 and 110. At the burn, the air gap is substantially greater and consequently the number of lines of force should be reduced as are indicated by the lines 112 and .114. It is thought that. the forward .edge 116 and the rear edge 118 of the burn develop in the sustained-field individuabpolarities and possibly :with adjacent walls havingopposite po1arities.--Thus 116 maybe a north--- and ll8 may be a south with lines of force such'as. 12f) extending between them and little'splmres of flux-at 122-- and 124. Applicants pickup 96 is a small coilson a vertical axis having a nonmagnetic core-andwextending lengthwise of the rail by /4 inch-over-all. In passing through the fields 120, 122 and 124, it-would generate asignalcomparable to that generated by small fissures.

Referring .now to Fig. 6, applicant shows the same field after demagnetization. llerethe-molecules in the skin of the rail are-arranged heterogeneously and the small-poles116 .and.118.will be recreated (by the sustainedfield if sufficient' time is permitted-r-to elapse.-

Hence; the pickup coil is mounted as close to the alternating current magnet 76 as-is consistent with staying out of any appreciablefield ofthat magnet.

Having thus. described my invention, Lclaim:

l. The method of detectingeinternal fissures-in a magnetizable body which comprises the steps of moving a magnet having one pole close to and the other pole substantially spaced fromthe body so as to create a flux circuitv through the body with lines of force leaving the body at angles declining from acute to right, and of checking 1 the density-and the direction of the flux circuit-adjacent the body at that point in the advancing flux circuit where the flux is leaving the body at approximately right angles.

to the surface of the body.

2. In that'method of detecting internal defects in amagnetizable body wherein a flux responsive means is passed through a flux field adjacent the body and sustained by an electric circuit generated 'by a means moving ahead of and with the flux responsive means, the step of moving a high frequency, alternating magnet along the body at a point in advance of the flux responsive means sufiiciently close thereto so that the time interval required by the flux responsive means to reach said point 2 appreciably penetrating the rail ata point in advance-ofv .7

the flux'responsive means sufficiently close thereto so that the time interval required by the flux responsive means to reach said point is insufiicient for the trailing sustained field-to repolarize the molecules in said skin.

4. The method of detecting internaljfissures in the ball of a' rail-which comprises the steps of moving magnetic poles of opposite polarity adjacent the rail ball at a selected speed so as to slowly oscillate the poles of the molecules-in the rail, of then moving a magnetic pole of one polarity-adjacent the rail ball so as to impress a directional set and polar-ize the molecules in the rail to create a trailing sustained field, of thereafter moving a high frequency, alternating magnetic current adjacent the surface of the rail so as to depolarize the skin of the rail ball withinthe trailing sustained field, and of passing a flux responsive means through the flux field adjacent said skin before the directional magnetization of the molecules deep in the rail within the trailing sustained field can re-establish'in the skin a polarization which will reflect obnormal conditions in the skin.

5. The method of detecting internal fissures in a rail ball which comprises the steps of subjecting the ball to a.

directional flow of fiux for x units oftime,-of immediately thereafter subjecting the ball to a reverse polarity for approximately 2x units of timeyof subjectingtthe ball to-the original. polarity, andwhile sustaining this polarity subjectingithe ball to from 25 to 50 reversals of polarity in less-\t-hanalx unitof time and'of moving immediately thereafter a fiuic responsive means through the field'adt jacent the. rail -ball.: 5 u

6. The'method of detecting internal 'fissures in a magnetizable'objectrwhich comprises the steps of polarizing a rail-ball in one direction for approximately one-half:

second; of then-polarizing the rail ball in the opposite direction for one and a halfseconds, of then polarizing the ball in the opposite or original direction-for two seconds, of concurrently'reversely polarizing the ball skin for 25 to 50- times in less than one secondfand'of immediately thereafter moving a time responsive means through the 7. The rnethod of detecting" internalfissuresin a rail which consists in moving a magnet adjacent the rail ball so as to create-a trailing sustainedmagnetic field, of subjecting the railball-in the trailing sustained field to a high-frequency flux circuit, and' of moving'a flux-re sponsive means through the trailing sustained field immediately after the fieldhasbeen subjected to the high frequency; circuit. 1

8. In the method of rail fissure detection wherein a flux responsive means' is passed through a trailing, weakening, electrically sustained flux field generated by a magnet moving-in advance-of the flux-responsive means,-the step of subjecting the rail ball within the trailing sustained field to an alternating.current magnet of a frequency of SOOto 1050 cycles imrnediatelydn' advance of the moving flux responsive means.

9. The method of detecting fissures in rails which comprises the steps'of moving 'a directional magnetizing force over the rail; of moving a magnetizing force of like strength but opposite p'olarity overthe rail after a lapse of x unitsof-time; of' moving amagnetizing force of the first polarity but'double'the'strength over the rail after a lapse .of 2x units of time, of then moving a magnet whose polarity'isi reversirrg"800 to 1050 times per second over the rail aftera lapse of 1 /15: units of time, and of then immediately-moving a flux responsive means through the field abovethe rail.

10. Apparatus for detecting fissures lying in rail track comprising two magnets longitudinally spaced by the distance x adjacent the rail and operably connected to the r car, a .third'magnetoperablyconnected to the car adjacent the rail and spaced rearwardly of the second magnet by azdistancer2x, an alternating current magnet mounted on the car -and spaced rearwardly of the third direct curr ent magnetby approximately the distance 196x; anda flux responsive means mounted on the car rearwardly of thealternating current magnet at a distance of A to /2x, the magnetic forces of the direct current magnets being such that'the flux responsive means lies in a trailing sustained field.

11. Apparatus for detecting fissures-lying in railroad track comprising a .car movable along the rails, a first and a second direct current magnet of like strength spaced longitudinally'along the rails by a distance x, a third magnet of double strength spaced longitudinally rearwardly of the second magnetby distance 2x, and a flux responsive means spacedfrom the third magnet by approximately 1 /2x,- the magnetic forces of the three magnets being such that the fiux responsive means lies in a trailing sustained field; I I

12. Apparatus for detecting fissures lying in rail track comprisingacar movable along the rails, three magnets mounted on the car and positioned adjacent the rail and longitudinally spaced from each other above one rail, the

polarity of the firstmagnet being north, of the second 10 magnet adjacent the rail and mounted on the car, and a References Cited in the file of this patent flux responsive means mounted on the ear rearwardly of UNITED STATES PATENTS the alternating current p t, said g a i g c ept 21927 Brace et a1 Oct. 21 1941 magnet and flux responslve means both bemg 1n 1hr: tmll- 2 218 784 Einstein Oct 22 1940 ing sustained field of the third magnet. 2,555,308 Bamgs June 5 1951 

